The present invention relates to a hydraulic circuit system mounted on a construction machine, such as a hydraulic excavator, including a plurality of hydraulic actuators which are often simultaneously operated, and more particularly to a hydraulic circuit system including a load sensing system and having control valves provided with flow distribution valves which enable a combined operation to be performed without being affected by a difference in load pressure between a plurality of hydraulic actuators.
JP,C 2721383 discloses a hydraulic circuit system employing a load sensing system in a hydraulic excavator as a typical example of construction machines, and including flow distribution valves which enable a combined operation to be performed. The hydraulic circuit system shown in FIG. 3 of the known art comprises a variable displacement hydraulic pump, a tilting control cylinder for the hydraulic pump, an LS valve for operating the tilting control cylinder depending on a differential pressure between a delivery pressure of the hydraulic pump and a maximum load pressure, and a flow distribution valve disposed on the outlet side of each meter-in throttle of a plurality of directional control valves. Further, a branch hydraulic line for detecting a load pressure is provided on the outlet side of each flow distribution valve, and a check valve is provided in the branch hydraulic line. With such an arrangement, when the load pressure of the associated hydraulic actuator is a maximum one, that load pressure is detected by the check valve and the detected load pressure is transmitted, as a signal pressure, to the LS valve via a signal transmitting hydraulic line. Also, a hydraulic fluid outgoing from the meter-in throttle is introduced to the hydraulic actuator through the flow distribution valve. The signal pressure is introduced to a control chamber in which a pressure bearing portion of each flow distribution valve acting in the throttling direction is positioned, and an inlet-side pressure of each flow distribution valve is introduced to a space in which a pressure bearing portion of each flow distribution valve on the opposite side (acting in the valve opening direction) is positioned. Thus, the same signal pressure is applied to the pressure bearing portions of all the flow distribution valves acting in the throttling direction, and the flow distribution valve on the lower load pressure side is balanced when the pressure bearing portion of that valve on the opposite side (acting in the valve opening direction) is subjected to the same pressure as the inlet-side pressure of the flow distribution valve on the higher load pressure side. Accordingly, a differential pressure across the meter-in throttle has the same value on both the higher and lower load pressure sides so that the hydraulic fluid delivered from the hydraulic pump is distributed depending on a ratio between valve openings of the meter-in throttles. With such a flow distributing function, the hydraulic actuators can be operated at the same time regardless of the difference in load pressure.
Also, a swing motor and a boom cylinder are provided as the hydraulic actuators, and an on/off valve is disposed in a branch hydraulic line for detecting a load pressure on the swing motor side. The on/off valve is operated by a pilot pressure signal for the boom-raising operation. With that arrangement, when the boom is raised while turning a swing body of the hydraulic excavator, the on/off valve is operated to cut off the load pressure of the swing motor, and the load pressure of the boom-raising operation is detected, as the signal pressure, to operate the LS valve and a pressure compensation valve.
Further, PCT Laid-Open Publication WO98/31940 discloses a control valve for use in a hydraulic circuit system including a load sensing system, the control valve being constructed as a valve assembly in combination of a flow distribution valve and a hold check valve for simplification. In the disclosed control valve, a valve body of the flow distribution valve is partly incorporated in a hollow valve body of the hold check valve, and a load-pressure detecting hydraulic line of the control valve is formed as an internal passage (hydraulic line slit) of the flow distribution valve. The internal passage is utilized to provide a check valve function. As a result, a check valve as a separate valve element is no longer required and the control valve is simplified in its construction.
Of civil engineering works using a hydraulic excavator, the most popular one is to scoop earth and sand excavated by a front device and to load the earth and sand on a dump truck. Let suppose the case of carrying out the work in such a manner that the truck is on standby with its bed positioned in a direction rotated 90 degrees from the excavating direction of the front device. After scooping the earth and sand by a bucket, the boom is raised to a level of the truck bed and an upper swing body is turned 90 degrees. Then, the work is finished by discharging the earth and sand onto the truck bed. To perform the work quickly, the upper swing body is turned simultaneously with raising of the boom. To avoid the hydraulic excavator from striking against the truck during the work, the bucket at a fore end of the front device must be at a position higher than the level of the truck bed when the upper swing body has been turned 90 degrees. A method of first turning the upper swing body through 90 degrees and then raising the boom accompanies a possibility that the bucket may strike against the truck bed.
In the hydraulic circuit system having the general construction shown in FIG. 3 of the above-cited JP,C 2721383 with the on/off switch not provided, when remote control valves for swing and boom-raising are both operated at the same time to perform the above-mentioned work, the upper swing body cannot move at once because it is an inertial body and a swing side system has large inertia. Therefore, the pressure detected on the swing side has a value close to a delivery pressure of a hydraulic pump, and the LS valve is operated to increase the pump delivery pressure up to a relief pressure immediately. In spite of that the boom can be operated with a lower pressure than the relief pressure when operated solely, an extra pressure loss (energy loss) is caused in a flow distribution valve portion on the boom side when the boom is operated simultaneously with the upper swing body. If the hydraulic circuit system includes a horsepower control function associated with the hydraulic pump, a pump delivery rate is reduced with an increase in the delivery pressure of the hydraulic pump. Unlike the case of moving an object vertically (i.e., the case where an object cannot be moved by a force less than the weight of the object), a load on the swing side corresponds to the case of moving an object on a horizontal plane. In this case, therefore, the load can be moved by a force greater than a frictional force between the object and the plane. In other words, though slowly accelerated, the upper swing body can be moved with the driving pressure in the boom side. To this end, it is desired that the pressure in the boom side be detected during the combined operation without detecting the pressure in the swing side.
In the hydraulic circuit system shown in FIG. 3 of the above-cited JP,C 2721383, the above-described function is achieved by operating the on/off valve, which is disposed in the branch hydraulic line for detecting the load pressure on the swing side, by the pilot pressure signal for the boom-raising operation so that the load pressure of the swing motor is not detected. The energy consumption and the working speed are thereby improved. In the disclosed prior art, however, it is required to provide a branch hydraulic line dedicated for detecting the load pressure, and to arrange the check valve in the branch hydraulic line. This raises a problem that a portion for detecting the maximum load pressure is complicated and the number of parts is increased, thus resulting in a higher cost.
With the control valve disclosed in the above-cited PCT Laid-Open Publication WO98/31940, as described above, a portion for detecting the load pressure is simplified by forming the load-pressure detecting hydraulic line of the control valve as the internal passage (hydraulic line slit) of the flow distribution valve, and utilizing the internal passage to provide the check valve function. The above-described problem that the portion for detecting the load pressure is complicated can therefore be overcome by employing the disclosed control valve in the hydraulic circuit system shown in FIG. 3 of the above-cited JP,C 2721383. In the case of forming the load-pressure detecting hydraulic line as the internal passage (hydraulic line slit) of the flow distribution valve and utilizing the internal passage to provide the check valve function, however, employing the arrangement of the disclosed hydraulic circuit system, i.e., providing the on/off valve to cut off the load pressure of the swing motor and detecting, as the signal pressure, the load pressure of the boom-raising operation on the lower pressure side during the combined operation of swing and boom-raising, implies not only that the load pressure of the swing motor is cut off (not detected), but also that the signal pressure (load pressure of another actuator) in the signal transmitting hydraulic line cannot be introduced to the control chamber of the flow distribution valve. Thus, the flow distributing function cannot be developed.
A first object of the present invention is to provide a hydraulic circuit system capable of detecting a pressure on the lower load pressure side, as a signal pressure, without cutting off a load-pressure detecting hydraulic line on the higher load pressure side during a combined operation in which an inertial body is driven.
A second object of the present invention is to provide a hydraulic circuit system capable of detecting a pressure on the lower load pressure side, as a signal pressure, during a combined operation in which an inertial body is driven, and capable of simplifying a portion for detecting a load pressure without impairing the flow distributing function.
(1)To achieve the above first and second object, the present invention provides a hydraulic circuit system comprising a hydraulic pump, a plurality of hydraulic actuators driven by a hydraulic fluid delivered from the hydraulic pump, a plurality of control valves disposed between the hydraulic pump and the plurality of actuators, a signal transmitting hydraulic line to which a signal pressure based on a maximum load pressure among the plurality of hydraulic actuators is introduced, and pump control means for controlling a delivery pressure of the hydraulic pump to be held higher than the signal pressure by a predetermined value, the plurality of control valves comprising respectively main valves including meter-in variable throttles for controlling flow rates of the hydraulic fluid supplied to the hydraulic actuators, and flow distribution valves disposed between the meter-in variable throttles and the actuators, each of the flow distribution valves including a valve body which has one end positioned on the inlet side of the flow distribution valve connected to the meter-in variable throttle and the other end positioned in a control chamber, the valve body being moved through a stroke depending on balance between a pressure in the control chamber and a pressure in the inlet side to control the pressure in the inlet side, thereby controlling a differential pressure across the meter-in variable throttle, wherein the hydraulic circuit system further comprises a load-pressure detecting hydraulic line provided in each of the plurality of control valves, the load-pressure detecting hydraulic line including a first hydraulic line with a check valve function, which is branched from a point between the meter-in variable throttle and the hydraulic actuator for detecting a pressure at the branched point, and is connected to the control chamber of the flow distribution valve, and a second hydraulic line for connecting the control chamber to the signal transmitting hydraulic line, the first hydraulic line with the check valve function including a valve body passage, which is formed in a valve body of the flow distribution valve and has one end being opened to one of the inlet side and the outlet side of the flow distribution valve and the other end being opened to an outer periphery of the valve body, and a lap portion located between the other end of the valve body passage and the control chamber and making the other end of the valve body passage opened to the control chamber when the valve body of the flow distribution valve is moved through a stroke of a predetermined distance in the valve opening direction; a selector valve provided in the second hydraulic line of the load-pressure detecting hydraulic line in a first particular control valve of the plurality of control valves; and a third hydraulic line connected to the outlet side of the flow distribution valve in a second particular control valve of the plurality of control valves, the selector valve having a first position at which a portion of the second hydraulic line on the side of the control chamber is connected to only the signal transmitting hydraulic line, and a second position at which the portion of the second hydraulic line on the side of the control chamber is connected to both the signal transmitting hydraulic line and the third hydraulic line.
Thus, the selector valve is disposed in the second hydraulic line of the load-pressure detecting hydraulic line for the first particular control valve, the second hydraulic line connecting the control chamber and the signal transmitting hydraulic line to each other. The selector valve has the second position at which the portion of the second hydraulic line on the side of the control chamber is connected to both the signal transmitting hydraulic line and the third hydraulic line which is connected to the outlet side of the flow distribution valve in the second particular control valve. When the selector valve is shifted to the second position during a combined operation (e.g., combined operation of swing and boom-raising) in which hydraulic actuators associated with the first and control valves are driven simultaneously such that the first particular control valve is on the side driving an inertial body (e.g., the swing side) and the second particular control valve is on the lower load pressure side (e.g., the boom-raising side), the signal transmitting hydraulic line is opened to the outlet side of the flow distribution valve in the second particular control valve as well during the combined operation. Therefore, the pressure in the outlet side of the flow distribution valve in the second particular control valve on the lower load pressure side is detected as the signal pressure by the signal transmitting hydraulic line.
When the pressure on the lower load pressure side is detected by the signal transmitting hydraulic line, the pump control means is operated so as to compensate the detected pressure, and the delivery pressure of the hydraulic pump is controlled to be kept higher than the pressure on the lower load pressure side. Accordingly, the flow distribution valve in the second particular control valve does not develop a throttling operation, and can prevent an extra pressure loss (energy loss) from being produced therein. Further, even when the pump control means includes a horsepower control function, a pump delivery rate is not reduced. As a result, the hydraulic fluid can be supplied to the side of the second particular control valve at a sufficient flow rate and good operability can be obtained in the combined operation.
Also, since the first hydraulic line with the check valve function is constituted as the valve body passage of the flow distribution valve and the valve body passage is utilized to provide the check valve function, a portion for detecting a load pressure of the control valve can be simplified.
In the case of constituting the first hydraulic line with the check valve function by utilizing the valve body passage of the flow distribution valve, cutting off the second hydraulic line, which connects the control chamber to the signal transmitting hydraulic line, implies not only that the pressure in the second hydraulic line is not detected, but also that the signal pressure in the signal transmitting hydraulic line (pressure of another actuator) is not introduced to the control chamber. Thus, the flow distributing function is not developed. With the present invention, the same function as resulted from not detecting the pressure on the side of the first particular control valve (pressure on the higher pressure side) is provided by, rather than cutting off the hydraulic line, connecting the control chamber to both the signal transmitting hydraulic line and the third hydraulic line (outlet side of the flow distribution valve in the second particular control valve). Therefore, a function of introducing the pressure on the side of the second particular control valve (pressure on the lower pressure side; signal pressure) to the control chamber on the side of the first particular control valve is maintained and the flow distributing function is not impaired.
(2)In above (1), preferably, the plurality of control valves further comprise respectively hold check valves disposed between the flow distribution valves and the hydraulic actuators, and the first hydraulic line with the check valve function is branched from a point between the meter-in variable throttle and each of the hold check valves to detect a pressure at the branched point.
With those features, even when the load pressure of the hydraulic actuator is increased beyond the pressure at the meter-in variable throttle of the main valve, the load pressure is held by the hold check valve and the hydraulic fluid is avoided from reversely flowing into a reservoir via the signal transmitting hydraulic line and the signal detecting hydraulic line.
(3)In above (1) or (2), preferably, the plurality of control valves each include a hydraulic line slit formed in the outer periphery of the valve body of the flow distribution valve and opened at one end to the outlet side of the flow distribution valve, the hydraulic line slit constituting the valve body passage.
Those features provide the valve body passage as a part of the first hydraulic line with the check valve function.
(4)In above (1), the hydraulic circuit system further comprises means for producing a first signal when the first and second particular control valves are both operated, and the selector valve is shifted from the first position to the second position by the first signal.
With those features, as mentioned in connection with above (1), the selector valve is operated so as to connect the control chamber to both the signal transmitting hydraulic line and the third hydraulic line, whereupon the pressure in the outlet side of the flow distribution valve in the second particular control valve on the lower load pressure side is detected as the signal pressure by the signal transmitting hydraulic line.
(5)In above (1), the hydraulic circuit system further comprises a check valve disposed in the third hydraulic line and allowing the hydraulic fluid to flow only in a direction toward the flow distribution valve of the second particular control valve from the selector valve.
With those features, when load pressures are reversed in magnitude during the combined operation such that the second particular control valve becomes the side providing a higher load pressure, the higher load pressure is detected as the signal pressure by the signal transmitting hydraulic line. As a result, the hydraulic actuator on the side of the second particular control valve can be positively driven.
(6)In above (5), the check valve is a pilot check valve capable of being selectively opened.
With that feature, when the hydraulic actuator on the side of the second particular control valve reaches its stroke end, the pilot check valve is opened so that the signal pressure in the signal transmitting hydraulic line is given by the pressure on the side of the first particular control valve. This feature contributes to providing a more appropriate working speed and reducing an energy loss.
(7)In above (6), the hydraulic circuit system further comprises means for producing a second signal when the hydraulic actuator associated with the second particular control valve reaches a stroke end, and the pilot check valve is opened by the second signal.
With those features, as mentioned in connection with above (6), when the hydraulic actuator on the side of the second particular control valve reaches its stroke end, the pilot check valve is operated to be open and the signal pressure in the signal transmitting hydraulic line is given by the pressure on the side of the first particular control valve.
(8)Further, to achieve the above object, the present invention provides a hydraulic circuit system comprising a hydraulic pump, a plurality of hydraulic actuators driven by a hydraulic fluid delivered from the hydraulic pump, a plurality of control valves disposed, between the hydraulic pump and the plurality of actuators, a signal transmitting hydraulic line to which a signal pressure based on a maximum load pressure among the plurality of hydraulic actuators is introduced, and pump control means for controlling a delivery pressure of the hydraulic pump to be held higher than the signal pressure by a predetermined value, the plurality of control valves comprising respectively main valves including meter-in variable throttles for controlling flow rates of the hydraulic fluid supplied to the hydraulic actuators, and flow distribution valves disposed between the meter-in variable throttles and the actuators, each of the flow distribution valves including a valve body which has one end positioned on the inlet side of the flow distribution valve connected to the meter-in variable throttle and the other end positioned in a control chamber, the valve body being moved through a stroke depending on balance between a pressure in the control chamber and a pressure in the inlet side to control the pressure in the inlet side, thereby controlling a differential pressure across the meter-in variable throttle, wherein the hydraulic circuit system further comprises a load-pressure detecting hydraulic line provided in each of the plurality of control valves, the load-pressure detecting hydraulic line including a first hydraulic line with a check valve function, which is branched from a point between the meter-in variable throttle and the hydraulic actuator for detecting a pressure at the branched point, and is connected to the control chamber of the flow distribution valve, and a second hydraulic line for connecting the control chamber to the signal transmitting hydraulic line; a selector valve provided in the second hydraulic line of the load-pressure detecting hydraulic line in a first particular control valve of the plurality of control valves; and a third hydraulic line connected to the outlet side of the flow distribution valve in a second particular control valve of the plurality of control valves, the selector valve having a first position at which a portion of the second hydraulic line on the side of the control chamber is connected to only the signal transmitting hydraulic line, and a second position at which the portion of the second hydraulic line on the side of the control chamber is connected to both the signal transmitting hydraulic line and the third hydraulic line.
With those features, as mentioned in connection with above (1), during a combined operation including driving of an inertial body, a pressure on the lower load pressure side can be detected as the signal pressure without cutting off the load-pressure detecting hydraulic line on the higher load pressure side. Therefore, an extra pressure loss (energy loss) can be prevented from being produced in a flow distribution valve portion and good operability can be obtained in the combined operation.